Using immutable data

After implementing and testing the library with real elevators, you find another bug—when someone physically keys into a session, sometimes they get deauthorized while still using the elevator. Sometimes is a terrible word to hear in a bug report.

Fixing the hard-to-reproduce bug

After way too much searching and researching, you find a test case that reliably reproduces the problem:

#[test]
fn invalid_deauthorization() {
   admin::reset_state();
   let session = admin::authorize_admin().ok();
   assert!(admin::authorize_admin().is_err());
   assert!(admin::is_admin());
}

Looking at this test case, the first thing we might ask is, why should this be permitted?

The problem that we encountered during physical...